PROTECTIVE ARRANGEMENTS ON THE EPIDERMIS. 317 the Sierra Nevada, and the mountains of Greece are unusually rich in such forms. If plants growing in such situations are protected against the dangers of too rapid and to9 abundant evaporation, how much more must this be the case in those regions where, with the increasing warmth of suraraer, the nuraber of showers steadUy dmiinishes; and where the soU becomes dried more and more deeply, so that aU the plants whose roots are near the surface are unable to derive a drop more water frora it ? All plants which are to survive the dry period in such places must during this time entirely cease transpiring—they must, as it were, tum into a chrysaUs and sleep during the suraraer. They actuaUy do this in aU sorts of different ways, and by the most diverse means. One of the comraonest and raost widely spread methods is, without doubt, by having the transpiring organs clothed with a thick covering of dry air-containing hairs. Plenty of examples of this are fumished by the flora of the Cape, Australia, Mexico, the savannahs and prairies of the New World, and the steppes and deserts of the Old. In the dry elevated plains of Brazil, Quito, and Mexico, there are large tracts covered with gregarious spurge- Hke growths and grey-haired species of Croton, and when the wind blows, raoving these bushes to and fro, undulations are set up over wide extents of country, the whole appearing like a biUowy sea of grey foliage. A sirailar picture is presented by the Paindras belonging to the Corapositae, or by the Lychnophora, on the high plains of Minas Geraes in Brazil. Nowhere in the whole world, however, does the presence of hairs on foliage, as a protection against exhalation, appear in such an abundant and varied manner as in the floral region surrounding the Mediterranean, known as the Mediterranean district. The trees have fohage with grey hairs; the low undergrowth of sage and various other bushes and semi-shrubs (for which the name " Phrygian undergrowth ", used by Theophrastus, may be retained), as well as the perennial shrubs and herbs growing on sunny hills and raountain slopes, are grey or white, and the preponderance of plants coloured thus to restrict evapora¬ tion has a noticeable influence on the character of the landscape. He who has only heard from books of the evergreen plants of the Greek, Spanish, and Italian floras, feels at the first sight of this grey vegetation that he has been in sorae degree deceived, and is terapted to alter the expression "evergreen" into "ever grey". Every conceivable sort of hair structure is to be raet with in these parts—coarse felt-work, thick velvet, and white wool mixed in endless variety. Here is a leaf looking as if covered with a cobweb; there another as if bestrewn with ashes or clay; here a leaf surface, covered with closely pressed hairs or scutiform scales, glistens like a piece of satin; and here again is a plant with such a long flock of hair that one raight imagine that sheep in passing had left pieces of their fleece hanging on it. There is- hardly a family in the flora of the Mediterranean district which does not possess members richly provided in this way. The Composites are the most reraarkable in this respect, especially the genera Andryala, Artemisia, Evax, Filctgb, Inula, andSdntoUna; then corae the Labiates of the genera Phlomis, Salvia, Teucrium,Marrubiu/m,. Stoochys, Sideritis, and Lavandula; rock-roses, bindweeds, scabious.